N-hydrocarbylthiophosphoric triamides and N-hydrocarbylphosphoric triamides are known to be effective urease inhibitors for use with urea-based fertilizer compositions. Note, for example, U.S. Pat. No. 4,530,714 to J. F. Kole, et al.
Known procedures for preparing N-hydrocarbylthiophosphoric triamides and N-hydrocarbylphosphoric triamides involve batch operations in which an N-hydrocarbylaminothiophosphoryl dichloride or N-hydrocarbylaminophosphoryl dichloride is formed in a first reaction, recovered, and often purified. In a second reaction, the N-hydrocarbylaminothiophosphoryl dichloride or N-hydrocarbylaminophosphoryl dichloride is reacted with ammonia to produce a slurry from which co-product ammonium chloride is separated by filtration. See for example, U.S. Pat. No. 4,530,714.
In commonly-owned copending U.S. application Ser. No. 08/786,396, filed Jan. 21, 1997, an excellent continuous process for the production of N-hydrocarbylthiophosphoric triamides is described. In one of its preferred embodiments, the process results in the formation of a concentrated solution of N-hydrocarbylthiophosphoric triamide in a mixture of a solvent (most preferably tetrahydrofuran) and a tertiary amine (most preferably triethylamine).
Unfortunately, N-hydrocarbylthiophosphoric triamides such as N-alkylthiophosphoric triamides, and N-hydrocarbylphosphoric triamides such as N-alkylphosphoric triamides are relatively unstable when subjected to elevated temperatures. Consequently, when recovering N-hydrocarbylthiophosphoric triamides from solutions in organic media such as ethers and/or tertiary amines, etc., using various conventional distillation procedures, the triamide tends to undergo an undesirable amount of thermal degradation. Not only is this wasteful of desired product, but the formation of thermally degraded species in the product reduces its purity and sales appeal. Alternative methods of recovering these triamides from solution such as crystallization and freeze drying can overcome the thermal decomposition problem but they are expensive to perform and involve troublesome solids processing. An efficient, cheaper method of overcoming these problems is desired.